1. Field of the Invention
This invention relates to systems and methods used for drying liquid ink images, and more particularly for a moving air jet for drying a liquid ink image in, such an apparatus as for example, a printer (e.g., as an ink jet printer or any black and white or color liquid ink printer), a facsimile machine that uses liquid ink development or an electrophotographic machine that employs liquid ink development (e.g. a xerographic copier).
2. Brief Description of Related Developments
In, for example, an ink jet apparatus the printing quality, such as, the uniformity of the ink density, the contrast of the ink with respect to the paper on which the ink is placed, or the lack of smearing, etc., is generally highly dependent upon the quality of the recording medium on which the ink is placed and also the surface tension of the ink. Inkjet printers that use a high surface tension recording medium, and therefore slow penetrating inks, including water soluble inks, require that care be taken to avoid smudging of the ink on the recording medium too soon after the ink is printed and to avoid offset problems, i.e., transfer of the ink onto an object that comes in contact with the recording medium, such as, for example, another piece of paper or a human hand. In general, it is desirable to be able to actively dry an inkjet printed image sufficiently so that the image bearing recording medium may be contacted by another object without there being smudging within 3 seconds after the image has been printed. Drying the printed ink is often accomplished naturally i.e., by ambient air drying, but active drying is also used, e.g., drying with a source of heat such as, for example, a radiant heater, a microwave heater, or a heated gas.
For example, U.S. Pat. No. 4,340,893 to Ort describes a scanning inkjet printer with an ink drying apparatus on the carriage where the drying apparatus includes a dryer body that directs unheated or heated air onto the printed ink, and even provides for re-circulation of the air. The humidity of the air may be monitored to obtain an indication of the drying capability of the system.
U.S. Pat. No. 4,970,528 to Beufort et al. discloses a uniform heat flux dryer system and method for an inkjet printer using an infrared bulb.
U.S. Pat. No. 5,349,905 to Taylor et al. teaches using a microwave dryer to dry a thermal inkjet printed image.
U.S. Pat. No. 5,502,475 to Kaburagi et al., teaches using an electrical resistance heater with a temperature control unit to dry an inkjet printed image.
U.S. Pat. No. 5,631,685 to Gooray et al. teaches using a microwave dryer for an inkjet printer. U.S. Pat. Nos. 5,713,138, 5,901,462 and 5,953,833 to Rudd teach the use of a dryer for wet coatings, including printing inks, the dryer using re-circulated, heated and pressurized air which impinges on the wet coated recording medium, and the use of energy emitters such as radiant heating elements.
U.S. Pat. No. 4,566,014 to Paranjpe et al. discloses a method of sheet feeding to enhance dryer operation, and discloses different types of dryers for ink drops on sheets, including a radio frequency dryer and a drying system employing dried and heated air blown at high velocity onto a sheet of paper to accelerate drying of the ink deposited on the sheet of paper.
U.S. Pat. No. 5,214,442 to Roller discloses an adaptive dryer which varies the feed rate of inkjet printed pages through a dryer and the temperature of the dryer, and also discloses a microwave dryer and a convective dryer.
U.S. Pat. No. 5,140,377 to Lewis et al. discloses a xerographic printing apparatus in which toner material is thermally fused and fixed onto a surface of a copy sheet by condensing water vapor on the surface of a copy sheet.
In commonly assigned and copending U.S. Ser. No. 09/721,736 filed Nov. 2, 2000 there is described a two-phase drying system and method for rapidly drying liquid ink that uses an active two-phase drying system. The invention separately provides for actively drying liquid ink using a brief water condensation interval to heat the liquid ink and recording medium, and following the water condensation interval, with a period of relatively low velocity laminar air flow, and following the laminar air flow, drying using a short period of modulated re-circulating hot air flow impinging on the wet ink. This results in the ink being dried in a rapid continuous manner equal to the printing rate so that no subsequent drying period is needed.
A general and basic requirement, in general, of liquid ink printers, particularly color printers, is that the previous image must be dried before a subsequent image can be written thereon. Drying can be achieved by using radiant energy to dry the fluid. However, this method is not preferred because of the long distance required for providing a heater in the process direction (requiring a long machine with a large footprint), and the possibility of fire or explosion due to the evaporating carrier fluid, especially if the carrier fluid or medium is flammable. Furthermore, the heated image-bearing medium may change its shape as the temperature thereof increases. This severely complicates, or makes impossible, the registration of the color separations.
Another drying method includes blowing room temperature air across the wet surface to vaporize the fluid. Due to the simplicity of this approach, this method is preferred in printers that operate at very low process speeds. However, very high flow rates or very high volumes of air will be required to dry images in high productivity applications, which makes this method somewhat impractical. Furthermore, this method may result in an image that is not uniformly dried across the process direction, leaving wet areas at the edges of the image.
With reference to FIG. 1, there is shown a schematic illustration of a conventional single pass color printer, generally indicated at 10, where a color image is created by superimposing color separations. The image processing involves passing a medium 11 over a writing head 12 to form a latent image for a first color 14. The medium 11 then passes over a development station 15 and a wet, visible image is created. The wet image is then moved past a drying station 16 which removes excess carrier fluid from the liquid image thereby preparing the image to receive the latent image for the next color 17. An example of this printer architecture is disclosed, for example, in U.S. Pat. No. 5,420,673. In such printers, room temperature air is blown across the wet image though a specifically designed channel to make more efficient use of the air. These dryers, although more effective than the dryers discussed above, present certain issues at high process speeds. The efficiency of these dryers is acceptable at high speeds only when the drying length is increased. Increasing the drying length however, results in a longer machine and larger footprint. Furthermore, sealing the air against a wide web is difficult and, as a consequence, this type of dryer becomes less efficient as air leaks past the medium.
One of the major issues that occur with many liquid ink drying techniques is the fact that after the drying process there are areas that are overdried and areas that are underdried. This is referred to as artifacts which show itself as image defects. The issue of artifacts arises frequently in high speed printing machines, e.g. a high speed ink-jet printer.
It is therefore a primary objective of the present invention to define a system and a technique (process) that can involve heating, cooling, drying, remoisturizing or any combination of these techniques, which avoids artifacts. The description which follows will focus on image drying where speed, safety and spatial uniformity are all required.
Quick and safe drying of wet images in accordance with the features of the present invention can be accomplished by the impingement of hot air flowing through many small jets (round nozzles) which move (i.e. are in motion) with respect to the image. This can be implemented by means of a suitable (i.e. considering both type of material and thickness) belt which has many holes in it, and whose movement (i.e. motion) can be independently adjusted. Air is supplied at a temperature that is sufficiently high to effect drying (approximately 200xc2x0 C.), but low enough to avoid scorching after prolonged exposure (i.e. something that could occur if there is a jam of the machine). Continuous and rapid movement (i.e. motion) of the jets relative to the image, ensures image drying uniformity and the absence of artifacts. The relative speed of the movement is suitably adjusted in accordance with optimum operating conditions. xe2x80x9cHole speedsxe2x80x9d can vary within a range dependent upon sheet speed. Hole speed might equal or be about 10 times faster than sheet speed. Hole velocity may be opposite of sheet velocity.
In accordance with the preferred features of the embodiments described herein, a dryer assembly for drying a liquid ink image formed on a substrate comprises a housing defining a portion of a sheet moving path; a plenum positioned within the housing, the plenum including air flow and outlet means contiguous to the plenum permitting forced air to exit the plenum. The outlet is in the form of a plurality of moving openings (i.e. opening in movement relative to the liquid ink image) that are adapted to direct flowing air through the openings while in movement to the liquid image. The openings thus move relative to the liquid ink image. A substrate transport device moves the substrate carrying the liquid ink image on a front side thereof through the housing and under the plurality of moving openings.
In accordance with another preferred feature of the embodiments described herein there is described an ink jet printing machine for printing a liquid ink image on a sheet of paper as it moves along a sheet path through a printing zone. The ink jet printing machine includes a frame; a printhead mounted to the frame and containing liquid ink for depositing an image onto the sheet of paper to form a liquid ink image thereon, a dryer assembly for drying the liquid ink image on the sheet of paper, the dryer assembly comprising (i) a housing defining a portion of the paper sheet moving path; (ii) a plenum positioned within the housing, the plenum including air flow and an outlet means permitting forced air to exit the plenum. The outlet is in the form of a plurality of moving openings (i.e. openings in movement relative to the liquid ink image) that are adapted to direct flowing air through the openings while in movement with regard to the liquid image. The openings thus move relative to the liquid ink image. A paper sheet transport device moves the paper carrying the liquid ink image on a front side thereof through the housing and under the plurality of moving openings. A controller is connected to a forced air feeding device for controllably blowing air onto the sheet, i.e. only when there is interrupted sheet movement through the housing of the sheet within the housing.